> From: Jan Beulich
> Sent: Thursday, August 19, 2021 4:06 PM
>
> While for context cache entry flushing use of did 0 is indeed correct
> (after all upon reading the context entry the IOMMU wouldn't know any
> domain ID if the entry is not present, and hence a surrogate one needs
> to be used), for IOTLB entries the normal domain ID (from the [present]
> context entry) gets used. See sub-section "IOTLB" of section "Address
> Translation Caches" in the VT-d spec.
>
> Signed-off-by: Jan Beulich
Reviewed-by: Kevin Tian
> ---
> Luckily this is supposed to be an issue only when running on emulated
> IOMMUs; hardware implementations are expected to have CAP.CM=0.
>
> --- a/xen/drivers/passthrough/vtd/iommu.c
> +++ b/xen/drivers/passthrough/vtd/iommu.c
> @@ -474,17 +474,10 @@ int vtd_flush_iotlb_reg(struct vtd_iommu
>
> /*
> * In the non-present entry flush case, if hardware doesn't cache
> - * non-present entry we do nothing and if hardware cache non-present
> - * entry, we flush entries of domain 0 (the domain id is used to cache
> - * any non-present entries)
> + * non-present entries we do nothing.
> */
> -if ( flush_non_present_entry )
> -{
> -if ( !cap_caching_mode(iommu->cap) )
> -return 1;
> -else
> -did = 0;
> -}
> +if ( flush_non_present_entry && !cap_caching_mode(iommu->cap) )
> +return 1;
>
> /* use register invalidation */
> switch ( type )
> --- a/xen/drivers/passthrough/vtd/qinval.c
> +++ b/xen/drivers/passthrough/vtd/qinval.c
> @@ -362,17 +362,10 @@ static int __must_check flush_iotlb_qi(s
>
> /*
> * In the non-present entry flush case, if hardware doesn't cache
> - * non-present entry we do nothing and if hardware cache non-present
> - * entry, we flush entries of domain 0 (the domain id is used to cache
> - * any non-present entries)
> + * non-present entries we do nothing.
> */
> -if ( flush_non_present_entry )
> -{
> -if ( !cap_caching_mode(iommu->cap) )
> -return 1;
> -else
> -did = 0;
> -}
> +if ( flush_non_present_entry && !cap_caching_mode(iommu->cap) )
> +return 1;
>
> /* use queued invalidation */
> if (cap_write_drain(iommu->cap))
